Real Time Display Overview
IRIS can output a real-time display (RTD) data stream using UDP data packets. You can use one of those provided or use your own.
The source code for the transmitter programs is in base/rtq_lib. The formats are documented in the sig_rtdisp.h file.
Any computer running IRIS on that network can receive and display the real time display data.
Because real time display is done in broadcast mode, it is scalable. If the IRIS Radar server sends real time display data, the load induced on the network, and the servers CPU is constant regardless of how many machines on the network receive and process the real time display data.
UDP data is not retransmitted upon packet loss. At the application level in IRIS, no attempt is made for detected packet losses nor are there any requests for retransmissions. If such a loss occurs at the transmitter, on the network, or at one or more receiving hosts, then a gap occurs in the picture drawn on the destination real time displays. This differs from IRIS product transmission which are done point-to-point via TCP and are reliable due to error checking and retransmissions.
The network load from a real time display server broadcasting is a function of the following:
| Dependency | Description |
|---|---|
|
Number of moments being broadcast |
Up to 3. Including Z, V, and W. |
|
Number of bins per radial |
The total number of bins, combined for all moments, is approximately 1400 per radial. There is an overhead of about 100 bytes per ray. |
|
Scan rate of the antenna |
Each bin requires one byte of data. A scan rate of 5 RPM (30 radials per second), requires about 1500 * 30 = 45000 bytes per second. Real time display bandwidth must be added to any other IRIS and other bandwidth being occupied on your network. |
The real time display data stream can be configured to transmit using up to 6 different formats, IP addresses, and ports. See the Setup utility documentation in IRIS and RDA Utilities Guide.
Normally, gateways such as multi-homed hosts, bridges and routers do NOT pass IRIS real time display data. This is because such devices are built to filter broadcast data. This keeps the real time display data on a single network. However, it is usually possible to configure such devices to pass broadcast data that occurs on a specific port (like the real time display port).
To receive real time display data, the receive process needs to issue a socket and a bind system call. Following this, the receiver can read messages from the socket as they are transmitted.